I'm not sure I agree that Thurber has been our best (American) humor writer, or our best short story writer. What about Raymond Carver? Doesn't Jon Stewart count?
Certainly, I find his writing humorous, but I also find it a bit monotonous. In this semi-autobiography, I tired easily of the bumblings in the dark. There were far, far too many of these stories. The electric car piece is hands-down the best of them all, but I feel he never achieves that level again in the "collection." His cartoons are consistently amusing, and since he started as a humorist in that arena, I wish he had further developed that.
However, it looks like I ought to try his short stories instead. Since it is mentioned in the short biography at the back of this book, I sought out "The Secret Life of Walter Mitty" and nearly died laughing. "Pocketa-queep"-- oh, my stars.
It could be that it's just too tough to write about your own life, and easier to make up someone else's. It sounds like his life was indeed difficult, at least towards the end (he went blind). While laughter is the best tonic, it felt to me as if he was either making up the humor in his strange family's turmoils or deliberately over-exaggerating it to allay the pain.